As is known there is a requirement for highly linear radio frequency (RF) energy power sensors which can be integrated on Microwave Monolithic Integrated Circuits (MMICs). One such requirement is associated with of a radio frequency (RF) amplifiers. In such an amplifier, a directional coupler is used to detect power reflected from an input tuner. A second coupler is used at the output to detect output power. An algorithm is used to provide automatic tuning in conjunction with outputs from other sensors on the chip. The operation of such a circuit is greatly simplified by use of detectors whose output is linear with power.
It is also preferred that these detectors, and their matching circuitry, be broadband to allow use over a wide range of frequencies. Broadband detectors can also be used to assess the input frequency band for a given signal. Here, several broadband power sensors are used to detect power in each of a plurality of smaller frequency bands. The couplers incorporate specific filtering to indicate the frequency detected.
A common detector implementation utilizes a Schottky diode. The diode is biased at a fixed forward dc current. The dc voltage required to maintain this current changes upon application of an RF signal. The effect relies upon the inherent non-linearity of the diode and is therefore very dependent on the power level applied. Any algorithm which utilizes the output of the diode must account for this non-linearity. This adds considerable burden to the process. It may also be necessary to calibrate individual detectors in order to maintain the robustness of the algorithm. The requirement of narrow band tuning circuits is an additional disadvantage of diode detectors. The output of such sensors will also be sensitive to the ambient temperature.